A5973AD

Additional features and protections

13/19

5

Additional features and protections

5.1

Feedback disconnection

In case of feedback disconnection, the duty cycle increases versus the maximum allowed

value, bringing the output voltage close to the input supply. This condition could destroy the

load.

To avoid this dangerous condition, the device is turned off if the feedback pin remains

floating.

5.2

Output overvoltage protection

The overvoltage protection, OVP, is realized by using an internal comparator, which input is

connected to the feedback, that turns off the power stage when the OVP threshold is

reached. This threshold is typically 30 % higher than the feedback voltage.

When a voltage divider is requested for adjusting the output voltage (see test application

circuit), the OVP intervention will be set at:

Equation 1

Where R1 is the resistor connected between the output voltage and the feedback pin, while

R2 is between the feedback pin and ground.

5.3

Zero load

Due to the fact that the internal power is a PDMOS, no boostrap capacitor is required and

so, the device works properly also with no load at the output. In this condition it works in

burst mode, with random repetition rate of the burst.

V

OVP

1.3

R

1

R2

+

R

2

---------------------

×

V

FB

×

=